A free-body diagram (Figure 4.3(b) in the text) shows the biomechanical system of interest, here the forearm-hand segment, isolated from the surrounding world. Forces acting on the segment are: the weight of the forearm and hand (Fg = m g) at their centre of mass, the muscle force (Fm) and the x- and y-components of the joint force (Fjx, Fjy), producing the three force equations of 4.1. Values that are known are as follows: m = 1.5 kg, r = 0.14 m, rm = 0.05 m and φ = 80Ëš. What is the value of Fjx?

Question

Quizplus · Accepted Answer

From the free-body diagram, we know that:
ΣFx = Fjx - Fm sin φ = 0 
ΣFy = Fg - Fjy - Fm cos φ = 0 
Στ = r × Fjy - rm × Fm = 0

Substituting known values and solving for Fjx, we get:

Fjx = Fm sin φ = (100 N) sin 80° ≈ 7.15 N

Therefore, the best choice is B.

A Free-Body Diagram (Figure 4